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Postponed means that the issue was either a feature request or something that requires major refactoring on our side. Since that makes the issue not actionable in the close future we choose to close it as Postponed and add it on our internal roadmaps and technical debt pages instead.




Found in


Issue ID




Every call to BuildAssetBundles recompiles scripts

Asset Bundles


To reproduce:
1. Open attached project
2. Press Assets > AssetBundles > Build Asset Bundles
The script will now build an asset bundle consisting of one image - test.png - a hundred times, and for each time it will display an additional set of warnings in the console, which suggests that scripts are recompiled when an asset bundle is built.

Note: The scripts being recompiled are not in the asset bundle, and the build target doesn't change, thus there is no need for the scripts to be recompiled.

Reproduced on: 5.5.0b1, 5.5.0f3, 5.6.0b2
Not reproduced on: 5.4.0f2, 5.4.3f1

Comments (6)

  1. 2da0ea29aed815433844222e8e3cf404?d=mm


    Jun 19, 2017 12:41

    it is reproduced also on 5.6.1p3. Please fix this asap. Building asset bundles now takes too long.

  2. B35c2b76ea4ff30e434fbb693aa2cbcd?d=mm


    Apr 03, 2017 19:26

    Is this fixed in 5.6? A real impediment to upgrading!

  3. 4d2c83242cc78a6535e82cc3a09eb26c?d=mm


    Feb 07, 2017 09:31

    I took a look into the Activity Monitor sampling on OSX, it showed that most of the build time on Unity 5.5 was spent on this function:

  4. B35c2b76ea4ff30e434fbb693aa2cbcd?d=mm


    Feb 02, 2017 22:16

    We have been testing our project under Unity 5.5.1f1 and have discovered that our bundle building process is about 10x slower than under Unity 5.4.2f1.

    This is the function that we call:

    BuildPipeline.BuildAssetBundles( bundleOutputDir, buildMap, BuildAssetBundleOptions.ChunkBasedCompression, target );

    Looking at the release notes for 5.5.0 I found this under known issue:

    Editor: Asset bundle building performance decrease when building multiple small asset bundles. (849376)

    This issue was among the fixes for 5.5.1f1:

    Asset Import: Fixed a bug when importing Alpha8 textures didn't import them as a single channel texture. (849376) - (it's odd that it says nothing about bundles)
    Unfortunately this does not fix the issue for us - we are still experiencing the slow bundle build problem.

    Upon further searching in the bug database we found issue 860738 "EVERY CALL TO BUILDASSETBUNDLES RECOMPILES SCRIPTS".…

    This issue could certainly explain what we are experiencing. Issue 860738 has a status of "postponed".

    Slow bundle building is a showstopper for our project as we use bundles extensively. Any assistance is greatly appreciated.

  5. E422b6043f99309c7664b2bd2046071c?d=mm


    Jan 07, 2017 14:58

    me too 5.5.0f3

  6. B36530eff44c377898b7fd8309cb6b05?d=mm


    Dec 22, 2016 22:44

    I'm using unity 5.5p3 and can confirm this is a bug. It's recompiling every time an asset bundle is created. This is accounting probably for the 10 x slowdown in asset bundle creation. I'm surprised no one else has been flagging this as a top priority fix for games with high asset build turn out.

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